1. Field of the Invention
The present invention relates to an optical information recording method and an apparatus, and more particularly to an optical information recording method and an apparatus provided with an improved mark-recording operation.
2. Discussion of the Background
In recent years, optical information recording apparatuses, such as a compact disk-recordable (CD-R) drive, have become commercially practical, and a study toward further increasing a storage capacity and a recording speed of the apparatuses is being continued. As recordable optical disk media, for example, a write-once optical disk medium using coloring agent compounds, a magneto-optical disk medium, and a rewritable optical disk medium using phase-change materials, are known.
In a general optical disk recording apparatus, laser light, which is emitted by a laser diode and pulse-modulated according to recording information, irradiates a recording medium, changes the reflection coefficient of the recording medium, and thereby forms a recorded-mark. The laser light power affects the quality or the state of the recorded-mark, i.e., if the quality of the recorded-mark does not satisfy the specification of a recording format, a data error occurs. Various states of the recorded-mark, for example, a horizontal shape, a cross-sectional radius of the hollow of the mark, the surface unevenness, the outline shape, the color, unevenness of the color, and so forth, are known. Therefore, hitherto, before starting an ordinary information recording operation, in order to determine a proper recording power suitable for the characteristics of a recording medium, test writing is carried out on a predetermined area of the recording medium while changing the recording power. The recording power that has recorded a signal, which is reproduced with the best symmetry, is chosen as an optimum recording power. The optimum recording power is maintained during ordinary information recording on a recording medium. This method is known as an “optimum power control” (OPC) method.
However, even when the optimum recording power, which is determined by the above-described test writing, is maintained during the ordinary information recording, other factors can disturb the accomplishment of an optimum recording. For example, the optimum recording power for recording depends upon the sensitivity of the recording medium, and therefore the optimum recording power changes according to variations in the sensitivity of the recording medium. Further, the optimum recording power changes according to a tilt of the recording medium relative to the laser light. In addition, even if a drive current of the laser diode is kept constant to keep the optimum output power for optimum recording, the actual output power of the laser diode may change due to, for example, an environmental temperature change, causing a deviation of the output power from the optimum output power for the optimum recording. In other words, even when a recording operation on a medium is performed using the conventional OPC method, an optimum recording might not be always possible throughout the whole area of the recording medium.
To solve these problems, for example, Japanese Patent Publication No.60696/1982 proposes to detect a change in reflected light of the recording light coming from the disk during an ordinary information recording operation. The output power of a light source is controlled in accordance with the result of the detection. According to this publication, while information is being recorded, the state of a recorded-mark is obtained at the same time based upon the result of detecting a change in reflected light from the disk, and thereby fluctuation of the recording power from an optimum recording power is detected. Such fluctuation may have been caused by variations in the output power of the light source in the recording operation, a tilt of the disk relative to the laser light, or variations in the sensitivity of the disk. The output power of the light source is controlled so that the fluctuation from the optimum irradiation power is compensated. More specifically, in a test writing operation, each recording power and a resulting detected signal indicating a change in the reflected light are stored in a corresponding manner, and in a normal writing, the laser diode is controlled so as to output the optimum output according to the stored information. A similar method, known as a “running-optimum power control” (R-OPC) method, is in use in some CD-R drive apparatuses.
The above method, i.e., controlling the output of a light source according to the result of detecting a change in reflected light from a recorded-mark, has however problems such that the reflected light does not change according to the recorded mark or such that the change in the reflected light can not be accurately detected under certain recording conditions or in a certain recording medium.
A reflection coefficient of a recorded area of a recording medium is different from that of the non-recorded area of a recording medium. Reflected light power is expressed as the product of irradiation light power and a reflection coefficient of a part of the recording medium covered by an irradiation light spot. During a recording operation, the irradiation light spot moves relative to the recording medium at a constant velocity on a recording track of the medium. Therefore, in the recording operation, the irradiation light spot always covers both a recorded portion, i.e., an area where a mark is formed, and a non-recorded portion of the recording medium in a certain ratio. Accordingly, the reflection coefficient of the area covered with the irradiation light spot can be determined as an average of those of the recorded portion and the not-recorded portion of the area of a recording medium covered by the irradiation light spot. However, in the recording process, the ratio of a recorded portion and a not-recorded portion of the area covered by the irradiation light spot dynamically changes for various reasons. For example, variation in the sensitivity of the recording medium changes the speed of forming the recorded mark. Accordingly, the result of detecting the change of the reflected light is apt to be influenced by any deviations in the sensitivity of the recording medium. Particularly, in a high-speed recording operation, the irradiation light spot mainly covers the non-recorded portion rather than a mark portion, and therefore, the reliability of detecting the change of the reflected light is apt to be decreased. Accordingly, the difficulty in accurately detecting the change of the reflected light increases in proportion to the recording velocity.
Further, when a multiple-pulse method, which is suited and is often utilized for a large capacity recording, is used as a method of forming a mark, a pulse train of a recording heating-pulse and a breaking bottom-power pulse is repeated in a short time. That is, the pulse is turned to the breaking pulse or the bottom-power pulse in a short time after reflected light of a recording pulse or a heating-pulse is received, and thereby reflected light is suddenly decreased. Therefore, a high speed detecting device and a circuit are required for an appropriate detection of the changes in the reflected light.